Monochromacy

Posted by Einstein Bear on
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This is how a Renault Bear would see a bunch of coloured crayons.

You might have noticed that our website is mostly black and white with little touches of red. They are the only colours used for a very special reason. Renault Bears are Monochromats. This is also known as “total colour blindness” and is a complete inability to distinguish between colours. There is one slight difference with Renault Bears though – we can also see red along with the more usual black and white. We think this is because our stable food is strawberry jam on toast. Over time – so the theory goes – we have developed the ability to see red because we have eaten so many strawberries. This is distinguished from more common forms of colour blindness, in which the affected individual can only perceive colour differences in greyscales. Let me try and explain this for you but it is quite complicated.

In the eyes of vertebrates there are typically two kinds of receptors: rods, which primarily distinguish between levels of illumination, and cones, which are responsible for the perception of colour. There are different types of cones; each perceives only a single colour. The normal explanation of monochromacy is that the organism’s retina contains only a single kind of light receptor cell, or at least that only one kind is active at any particular level of illumination. Monochromacy is caused by either a defect or the complete absence of the retinal cones.

Some individuals possess diseases or injuries that lead to nyctalopia, or night blindness, where rod cells stop responding properly to light.

There are two known types of monochromacy. Animals with monochromatic vision may be either rod Monochromats or cone Monochromats. These Monochromats contain photoreceptors which have a single spectral sensitivity curve. There is also a third, theoretical type that has never been identified.

Rod monochromacy is the condition of having only rods in the retina. A rod Monochromat is truly unable to see any colour and can see only shades of grey.

Cone monochromacy is the condition of having both rods and cones, but only a single kind of cone. A cone Monochromat can have good pattern vision at normal daylight levels, but will not be able to distinguish hues. In humans, who have three different types of cones, there are three differing forms of cone monochromacy. There are three types named according to the single functioning cone class:

  1. Blue cone monochromacy, also known as S-cone monochromacy
  2. Green cone monochromacy, also known as M-cone monochromacy
  3. Red cone monochromacy, also known as L-cone monochromacy

Cone monochromacy, type II, if its existence were established, would be the case in which the retina contains no rods, and only a single type of cone. Such an animal would be unable to see at all at lower levels of illumination, and of course would be unable to distinguish hues. In practice it is hard to produce an example of such a retina, at least as the normal condition for a species.

It used to be confidently claimed that most mammals other than primates were Monochromats. In the last half-century, however, evidence of at least dichromatic colour vision in a number of mammalian orders has accumulated. Two of the orders of sea mammals, the pinnipeds (which includes the seal, sea lion, and walrus) and cetaceans (which includes dolphins and whales) clearly are cone Monochromats, since the short-wavelength sensitive cone system is genetically disabled in these animals. The same is true of the owl monkeys, genus Aotus.

Both rod and cone monochromacy occur as very rare forms of colour blindness in humans. Rod monochromacy, or maskun, is the more common of the two. The majority of people described as colour blind, however, are either dichromats or anomalous trichromats.

According to Jay Neitz, a renowned colour vision researcher at the University of Washington, each of the three standard colour-detecting cones in the retina of trichromats — blue, red and green — can pick up about 100 different gradations of colour. The brain can process the combinations of these three values so that the average human can distinguish about one million different hues (100x100x100=1million). Therefore, a Monochromat – like Renault Bears – can only distinguish between 100 shades.

I hope that made sense.


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About the Author

Einstein Bear

I was rescued from eBay back in 2007 and brought to our retirement home to join the other Bears. I quickly settled in and realised what a great gang of bears we have here. During my first few days, everyone decided that because I was relatively intelligent, I would be christened Einstein. I like reading the newspapers and watching the news so it seemed to fit.


2 Comments on “Monochromacy”

    1. We have a bearkeeper who looks after us. His name is Davidd. He makes us our Jammy Toast and looks after us. We will have to write a story about him to introduce him.

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